(1) Field of the Invention
The present invention relates to a rack structure that includes a plurality of shelves arranged vertically each for accommodating a plurality of printed circuit boards on which electronic devices are mounted, parallel to each other, and more particularly to a rack structure that is configured to cool printed circuit boards by forced ventilation using fans, and a communication apparatus employing the rack structure.
(2) Description of the Related Art
A conventional communication apparatus is constructed by vertically arranging a plurality of shelves for accommodating a plurality of printed circuit boards on which electronic devices are mounted, parallel to each other, and is installed e.g. in a base transceiver station. The electronic devices include heat-producing elements. Therefore, fans or the like are provided between vertically adjacent ones of the shelves to form a ventilation structure for cooling (e.g. Japanese Unexamined Patent Publication No. 8-167784.
FIG. 17 is a perspective view of an example of the construction of such a conventional communication apparatus 101, and FIG. 18 is an exploded perspective view of the communication apparatus. Further, FIG. 19 is a cross-sectional view taken on line A-A of FIG. 17, and arrows represent flows of air by forced ventilation.
As shown in FIG. 17, the communication apparatus 101 is constructed by arranging shelves 103, 104, and 105, fans 106, 107, and 108, and heat shield plates 109 and 110, etc. within a rack 102 comprising a frame formed by welding sheet metal components.
As shown in FIG. 18, the shelves 103 to 105 accommodate a plurality of printed circuit boards 111, 112, and 113, on which electronic devices are mounted, parallel to each other, and these printed circuit boards are mounted on a mother board 114 provided on each shelf and have electrical functions.
As shown in FIG. 19, the shelf 103 is cooled by forced ventilation by the fan 106, and on the other hand, a heat shield plate 109 is arranged between the two shelves 103 and 104, for preventing exhaust heat from heating the shelf 104 disposed immediately above. The heat shield plate 109 has a partition plate 115 for diagonally partitioning between a lower exhaust passage for exhausting warm air exhausted from the shelf 103 via the fan 106, to the rear side, and an upper introduction passage for passing outside air from the front side into the shelf 104, and is arranged such that the heat shield plate 109 covers the fan 106 from above. When the fan 106 disposed above the shelf 103 is driven, outside air is drawn up from below, and the air for cooling circulates through the shelf 103 to cool the printed circuit boards 111 disposed therein. At this time, although the air used for cooling is increased in temperature by heat exchange occurring when cooling the printed circuit boards 111, it is exhausted to the outside of the apparatus after flowing along the partition plate 115 of the heat shield plate 109. Therefore, the warmed air does not adversely affect the shelves 104 and 105 disposed above.
Further, the shelf 104 is also cooled by forced ventilation by the fan 107, and so as to prevent the exhaust heat from heating the shelf 105 disposed immediately above, a heat shield plate 110 is disposed between the shelves 104 and 105. Then, outside air is drawn into the upper introduction passage of the heat shield plate 109, and the air for cooling circulates through the shelf 104 to cool the printed circuit boards 112 disposed therein. At this time, the air used for cooling is increased in temperature by heat exchange, and flows along the partition plate 115 of the heat shield plate 110 to be discharged to the rear side of the apparatus.
Further, in the shelf 105 as well, air is drawn into the upper introduction passage of the heat shield plate 110 from the front by forced ventilation by the fan 108, and the air for cooling circulates through the shelf 105 to cool the printed circuit boards 113 disposed therein. At this time, the air used for cooling is increased in temperature by heat exchange, and is delivered from the fan 108 to be exhausted from an opening formed in an upper end of the apparatus.
By the way, recently, the communication apparatus described above requires larger capacity and larger output, and accordingly, the number of printed circuit boards accommodated therein increases to increase electric power consumption. Therefore, to maintain the heat-dissipating efficiency of the apparatus, countermeasures have conventionally been taken e.g. by increasing the number of fans disposed in the rack, employing highly efficient fans having large outside dimensions, and increasing the rotational speed of fans.
However, in actuality, the dimensions of the rack of the communication apparatus are limited such that the apparatus can be installed in a specified installation space, and hence it is impossible to easily increase the number of fans, or increase the dimensions of fans, which makes it very difficult to secure the cooling performance. Further, an increase in the rotational speed of fans causes another problem of increased noise.